The present invention relates to a process for reducing harmful components in the waste gas exhausted from an internal-combustion engine and for increasing the power supplied by the engine through the recycling of a portion of the waste gas.
The implementing of the process notably enables meeting to the ever stricter standards applied to spark-ignition engines. As a matter of fact, studies have shown that the recycling of a portion of the gas exhausted from the cylinders not only causes a reduction in the nitrogen oxides emitted, but also a significant decrease in the amount of unburned hydrocarbons at the end of the exhaust phase. The main difficult to be solved is the control of the flow of recycled gas according to the working conditions of the engine.
The principle of the taking of a fraction of the gas burned by an engine in the exhaust pipes and the reintroducing thereof, after cooling, into the inlet channels of the cylinders in order to decrease the discharge of certain harmful components is well-known. Such a recycling can be implemented in several ways.
For example, in CH 530,554, a process and a device for allowing recycling of exhaust gas is proposed wherein a partial re-opening of the exhaust valves during the phase of intake of fresh gas enables a redrawing of a portion of the exhausted waste or exhaust gas into each cylinder at the end of the previous combustion cycle. This process is essentially implemented by modifying the shape of the cams controlling the exhaust valves in order to impose an additional partial re-opening. This process, which is applied to engines having two valves per cylinder, does not allow the attainment of an optimum effect, whatever the working conditions of the engine may be, because the partial re-opening of the exhaust valve is imposed by the shape chosen for the actuating cam and is therefore immutable in many cases.
Processes for improving the efficiency of an engine and having the effect of meeting the standards for exhaust gas discharge are also well-known, with these processes being implemented in engines equipped with a double inlet valve per cylinder and being based upon the principle of modulation of the air flow passing through one of the two inlet valves. The prior art for this type of engine is, for example, described in an article of SAE Technical Paper Series No. 900,227 by Mikulic et al.
U.S. Pat. No. 4,173,203 describes a system for decreasing the exhaust gases discharged from an internal-combustion engine comprising, per cylinder, an additional inlet valve connected with an air inlet circuit comprising a pump, a tank for stocking the air compressed by the pump and an auxiliary circuit allowing a diversion towards the pump inlet a controlled part of the exhaust gas of the engine.
Patent DE 3,146,654 describes an analogous system wherein a controlled part of exhaust gas is reinjected into the cylinders through an auxiliary valve after being compressed and stored in a storage capacity.
Experience shows that the rate of harmful discharges varies during each exhaust phase, with a peak towards the end of this phase, and that the decrease in harmful discharges is stronger if these peaks can be more particularly recycled. The existence of a rather long recycling circuit with means for the compression and the storing of fractions of waste gas has the effect of diluting the peaks in question. The effect of the recyclings on the harmfulness of the discharges is therefore reduced. This dilution may even lead to a degradation of the combustion and, moreover, to an increase in the rate of unburned hydrocarbons.